My husband and I stayed in the area overnight and stopped by the park in the morning before we got back on the road to New Orleans. It was well worth the time. I believe we were on the first tour that day (9:20am), as we read that it was important to get there early because tours fill up quickly. They only allow up to 25 people/tour, and when you get inside, you understand why.
From their site: "The park is open from 8:00 a.m. until sundown, 365 days a year. Cave tours are not available on Tuesday, Wednesday, Thanksgiving Day and Christmas Day." Cave tours start at 9:00 am.
Once we were on the tour, we were told that they get a lot of school groups in, so it may be a good idea to call ahead to make sure you're not in one of those groups, only because they advised it can get very loud in the caves with lots of small, excited children.
The scenery inside the cave is incredible - very other-worldly. Bring a camera that works well in low-level lighting. The tour guide gave great educational information, but if you're nerds like us and want to study up a bit beforehand, there's a quick video in the information center that gives all of the same information as the tour guide provides.
There are times where you have to bend down to get through lower areas, so you might want to do your back stretches ahead of time if you have issues. There were several older people on our tour, and I heard them complain a bit, but nothing that would preclude them from finishing the tour. It can get a little chilly, as you can imagine underground, so think about bringing a light sweater or jacket. I would probably stay away from wearing flip-flops if you can help it since there were some slightly wet/muddy areas.
We also ventured to another beautiful part of the park, near the horse camp. I would recommend allotting a little extra time to wander other areas of the park and trails.
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